Fixes to support Python 2.6 again.

Details:

- Added Python 2.6 again to .travis.yml (it was removed in commit 4486bcb).

- Replaced the use of dictionary comprehensions in `git/cmd.py` around
  line 800 with the code before that change (in commit 25a2ebf).
  Reason: dict comprehensions were introduced only in Python 2.7.

- Changed the import source for `SkipTest` and `skipIf` from `unittest.case`
  to first trying `unittest` and upon ImportError from `unittest2`.
  This was done in `git/util.py` and in several testcases.
  Reason: `SkipTest` and `skipIf` were introduced to unittest only
  in Python 2.7, and `unittest2` is a backport of `unittest` additions
  to Python 2.6.

- In git/test/lib/helper.py, fixed the definition of `assertRaisesRegex`
  to work on py26.

- For Python 2.6, added the `unittest2` dependency to `requirements.txt`
  and changed `.travis.yml` to install `unittest2`. Because git/util.py
  uses SkipTest from unittest/unittest2, the dependency could not be added
  to `test-requirements.txt`.

- Fixed an assertion in `git/test/test_index.py` to also allow
  a Python 2.6 specific exception message.

- In `is_cygwin_git()` in `git/util.py`, replaced `check_output()` with
  `Popen()`. It was added in Python 2.7.

- Enabled Python 2.6 for Windows:

  - Added Python 2.6 for MINGW in .appveyor.yml.

  - When defining `PROC_CREATIONFLAGS` in `git/cmd.py`, made use of certain
    win32 and subprocess flags that were introduced in Python 2.7, dependent
    on whether we run on Python 2.7 or higher.

  - In `AutoInterrupt.__del__()` in `git/cmd.py`, allowed for `os` not having
    `kill()`. `os.kill()` was added for Windows in Python 2.7 (For Linux, it
    existed in Python 2.6 already).

1 files changed, 5 insertions, 0 deletions

diff --git a/.travis.yml b/.travis.yml
index f7dd247b..a3f8c705 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,10 +1,14 @@
 language: python
 python:
+  - "2.6"
   - "2.7"
   - "3.3"
   - "3.4"
   - "3.5"
   # - "pypy" - won't work as smmap doesn't work (see gitdb/.travis.yml for details)
+#matrix:
+#  allow_failures:
+#    - python: "2.6"
 git:
   # a higher depth is needed for most of the tests - must be high enough to not actually be shallow
   # as we clone our own repository in the process
@@ -15,6 +19,7 @@ install:
   - git fetch --tags
   - pip install -r test-requirements.txt
   - pip install codecov sphinx
+  - if [ "$TRAVIS_PYTHON_VERSION" == '2.6' ]; then pip install unittest2; fi
 
   # generate some reflog as git-python tests need it (in master)
   - ./init-tests-after-clone.sh